At a divergent tectonic boundary, what type of economic deposits would you expect?

• A. Evaporites
• B. Kimberlites and Carbonatites
• C. Porphyry copper deposits
• D. Massively layered sulfide deposits

Answer: (B)

Divergent boundaries create extensional settings where mantle upwelling and decompression melting produce mantle-derived, volatile-rich magmas. Kimberlites and carbonatites come from deep mantle sources and ascend rapidly through the crust in these extensional environments. Kimberlites are famous for carrying diamonds from deep within the mantle to the surface, while carbonatites are carbonate-rich magmas that often host rare earth elements and other ore minerals. The combination of mantle origin and continental rifting at divergent boundaries makes these two rock types especially associated with such settings, so they’re the best fit for the expected economic deposits there. Evaporites form in restricted basins with arid climates, porphyry copper is linked to subduction-related arc settings, and massive sulfide deposits are classic at mid-ocean ridges, but the pairing of mantle-derived, alkaline, diamond- and REE-bearing rocks aligns most closely with divergent boundary extensional magmatism.